Obsidian is formed when lava from a volcanic eruption cools rapidly. The resulting volcanic glass has excellent fracturing properties and was highly desired by ancient toolmakers and users. Obsidian sources have distinctive chemical signatures, allowing archaeologists to figure out the source of obsidian artifacts and trace their movement. In 1946, UMMAA archaeologist James B. Griffin collected the prismatic core and fine blades shown here from the site of Culhuacan (AD 600–1500) in the Valley of Mexico. The greenish tint of the material, most visible on the central blade, suggests it comes from Pachuca, about 30 miles northeast of modern Mexico City. Pachuca obsidian was especially renowned for its purity and superb flaking properties and was widely traded throughout ancient Mesoamerica.
In honor of the University of Michigan’s 2017 bicentennial, we are celebrating the remarkable archaeological and ethnographic collections and rich legacy of research and teaching at the Museum of Anthropological Archaeology by posting one entry a day for 200 days. The entries will highlight objects from the collections, museum personalities, and UMMAA expeditions. The Kelsey Museum of Archaeology is also posting each day for 200 days on Twitter and Facebook (follow along at #KMA200). After the last post, an exhibition on two centuries of archaeology at U-M opens at the Kelsey. Visit the exhibit—a joint project of the UMMAA and the Kelsey—from October 18, 2017 to May 27, 2018.